Paraffins are organic compounds which are a natural component of crude oil. They consist of various forms and combinations of aliphatic hydrocarbons and asphaltenes, form complex paraffins, and are characterized by their relatively high melting points and cloud points. At high temperatures, paraffinic crude oil flows freely through oil wells, wellbore tubulars and conduits carrying the oil. However, at temperatures below approximately 45° C. the paraffins begin to precipitate and form wax or paraffin deposits on the inner walls of the oil wellbore tubulars. These deposits grow thicker and more complex due to deposition of clay and corrosion products along with paraffins and asphaltenes. Eventually this buildup results in a significant narrowing or complete blockage of the oil wellbore tubulars, causing the crude oil flow through the wellbore tubulars to decrease markedly or to stop entirely. These paraffin deposits cause a loss of billions of dollars per year world wide due to the enormous cost of prevention and remediation, reduced or deferred production, well shut-in, pipeline replacements and/or abandonment, equipment failures, extra power requirement and increased man power needs.
Existing techniques for control of paraffin deposition in oil wellbore tubulars tend to be expensive and are plagued by a variety of problems. Hot water, chemicals and solvents that are customarily used to dissolve the paraffin deposits are costly, can be environmentally hazardous. In some instances wellbore tubulars have burst due to pressure build-up during a wax removal process. Periodic mechanical scraping of wellbore tubulars are commonly employed, however, those methods can require frequent shut downs of the well with associated production losses. Circulation of hot oil and hot water have also been employed, usually with only marginal success. There has been a great deal of activity in the field of preventing paraffin deposition and wax removal from the oil wellbores to deconstrict the oil wellbores and improve oil flow.
Currently, several methods and techniques are conventionally used for wax removal. These fall into three broad categories, the first of which includes temperature sensitive hot oil and hot water techniques. The second category includes mechanical scraping of the deposited wax, and the third category includes chemical methods. The hot oil technique for wax removal tends to be limited in applicability as it is usually effective only in the incipient stages of wax deposition. Hot oil treatment usually ceases to work in cases where wax deposition has already progressed and blocked the oil well. In situations where hot oil treatment alone is employed, the frequency of treatment is typically high in order to adequately control the wax buildup problem. The mechanical scraping of wax deposits from an oil wellbore is usually more time consuming than other methods, and also requires a shut down of the oil well for wax removal. The third category, chemical methods, typically involves the use of various surfactants and solvents. Aggressive blends of aromatic and/or aliphatic petroleum hydrocarbons or halogenated hydrocarbons, and water-based alkaline, hard-surface cleaners have been used for cleaning oil well buildups such as paraffin.
A fourth technique which has been suggested for decreasing wax buildup in oil well tubing involves the use of microbes. Some have proposed the use of bacteria to digest paraffinic and tar-based soils. The latter is said to be very dependent on well temperature and salinity and is sensitive to environmental factors such as the composition of the oil. Such bacteria-based solutions usually require that the well be shut down for several days to allow the establishment of a bacterial colony. When pumping resumes the bacteria are removed with the oil, which results in rapid depletion of the colony, thus necessitating repeated treatment. There is continued interest in developing ways to remove existing paraffin wax deposits from oil wellbore tubing and to prevent its deposition, in order to enhance oil recovery. Methods that minimize the need for shutting down production and that reduce the need for frequent retreatment are especially sought.